Method and arrangement to monitor a fatty oil treatment process carried through under vacuum

ABSTRACT

The present invention is a method and apparatus for monitoring the vacuum conditions for the treatment of vegetable or animal oil. During the treatment, a number of processes, such as refining, bleaching and/or deodorization, are carried out under a vacuum. The vacuum is maintained by a vacuum system, comprised of at least one vacuum creating means and at least one condenser, and a pump arranged at the outlet of the condenser. The condenser is connected to a mass flow meter monitoring the flow of a gas and generates a signal receivable by a controller. The method of monitoring the vacuum system, using the above apparatus, includes the steps of sensing, and registering the mass flow of non-condensable gas out of the vacuum system. An alarm is triggered when the amount of gas exiting the vacuum system differs from a set value.

FIELD OF THE INVENTION

The present invention relates to a method to monitor a process fortreatment of vegetable or animal oils such as refining, bleaching ordeodorization, in which process a number of process steps are carriedthrough under vacuum created by a vacuum system. The invention alsorelates to an arrangement to carry through the proposed method.

BACKGROUND OF THE PRESENT INVENTION

When producing vegetable or animal oils from different raw materialsthere are usually a number of process steps, where the oil is treatedunder vacuum with or without stripping gas. The aim of these processsteps is to remove substances that impart disagreeable odours and taste.These substances may have been formed during different earlier treatmentsteps or may have been present already in the cruel oil. The result ofthis vacuum treatment is to a high degree dependent on really obtainingthe desired vacuum level. The vessels in which the vacuum treatmenttakes place are usually of imposing size. A large plant may for examplehave a vessel with a height of 35 meters and a diameter of 3 meter.Usually, the vacuum vessels are provided with vacuum meters to controlthe vacuum.

Often a number of vacuum vessels, in which the oil is treated, areconnected to a common vacuum source. This may consist of a vacuum systemcomprising vacuum generating means and condensers. The vacuum generatingmeans may consist of a vacuum pump or of a steam ejector. In largeplants a number of steam ejectors with intermediate condensers are oftenused. The condenser is chilled with water, distillate or some othersuitable liquid in order to achieve condensing of condensable gases.

In EP 513 739 there is shown a deodorization system with vacuum boostersand condensers, which equipment makes it possible to reach the highvacuum that is necessary for carrying through the treatment. Accordingto this prior art the non-condensable gases are discharged to theatmosphere.

The vacuum system operates to achieve a vacuum level of 0,5-6 mbar inthe different vessels and heat exchangers used during the treatment ofthe fatty oil. The added stripping gas as well as dissolved gases in theoil and various compounds formed during the treatment are removed fromthe treatment vessels.

An efficient treatment of the fatty oils requires the mentioned vacuumlevels. The vacuum value is usually monitored by a pressure sensor.Working at this high vacuum means that the instrument used for sensingthe pressure firstly must be evacuated to absolute vacuum and that thepressure in the vessel is then measured in relation to absolute vacuum.

Some leakage in the equipment or in the pumps or valves, which arenecessary to build up the plant, will result in problems to obtain thedesired vacuum value. Air leaking into the vessel will also causeundesired oxidation and may lead to spoiled products.

One aim of the present invention is to bring about an accurate and rapidcontrol of the vacuum value in the equipment, another to make itpossible to obtain an early detection of any faults in the vacuumsystem. The present invention also means that start-up of a plant may bedone in a much shorter time than according to prior art.

SUMMARY OF THE PRESENT INVENTION

According to the method of the present invention it is now proposed thatthe mass flow of non-condensable gas out from the vacuum system iscontrolled and registered. During steady-state operation in a tightplant the mass flow through the mass flow meter will be constant. Thestripping gas is added in a known and constant amount. If the strippinggas consists of steam it is condensed in the condensers in the vacuumsystem. If some inert gas is used for stripping the flow ofnon-condensable gas will be greater but the value will be a constant oneif the equipment functions.

An arrangement in a plant for carrying through the method according tothe invention comprises a vacuum system with at least one vacuumcreating means and at least one condenser and a mass flow meter for gas,which by way of a pump is connected to the last condenser in the vacuumsystem. Mass flow meters of a suitable kind are available on the market.

According to the method of the invention it is possible to control theamount of gas which passes the mass flow meter all the time. Duringoperation conditions the mass flow is constant and represents thecontent of non-condensable gases in the stripping gas. Should this valuebe changed but the pressure remain constant there is a leakage somewherein the plant.

When the plant is new or shall be started again after a stop the vesselsand other equipment put under vacuum is evacuated, after which thevacuum system is cut off. If there is an increase in pressure there is aleakage in the plant. Often one starts by controlling each separatevacuum vessel and thereafter the whole plant. This is circumstantial andmay demand from some days up to several weeks in leak searching if thetests must be redone.

According to the method of the invention the evacuation process may becontrolled and if the pressure (in relation to the mass flow) in theequipment is not lowered at the rate, which may be expected knowing thecapacity of the vacuum system, one obtains an early indication thatthere is a leakage somewhere or there is something wrong with the vacuumsystem.

The proposed method gives alarm far more early than the generally usedmethod of monitoring only the pressure.

BRIEF DESCRIPTION OF THE DRAWING

The proposed invention is described further with reference to adeodorization plant chosen as an example only, which plant isschematically illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The Alfa Laval deodorization plant, which is shown very schematically,only shows equipment, which is of importance in connection with theinvention. Neither pumps, valves, all heat exchangers, strippingequipment nor control equipment are shown.

Oil 1, which is to be treated in the plant, is preheated in a heatexchanger 2 by treated oil 3 with a high temperature, which oil has beentreated in the plant. The arriving oil flows through the heat exchangerin tubes, which are surrounded by treated oil, which is thereforechilled. Stripping gas, steam or some inert gas is injected into thetreated oil. The gas leaves through a tube 4, which is connected to thevacuum system. The preheated oil 5 is directed further to an additionalheat exchanger 6, where the oil is heated to a desired high temperatureby means of steam. Also in this heat exchanger stripping gas, which isevacuated by way of tube 7, is added. The heated oil 8 is directed tothe deodorization column 9 from the heat exchanger 6.

In this column 9 oil flows downward firstly through an upper spacefilled with a structured packing material and then through a number oftrays in the lower part of the vessel. Also in this column the oil istreated with stripping gas in a number of places in the column. Thedeodorization column 9 is evacuated by way of a tube 10. The tube 4leads to the deodorization column 9 and the heat exchanger 2 isconsequently evacuated by way of the column 9. The tubes 7 and 10 leadto a vessel 11, which is chilled by distillate and in which oil havingfollowed the gas stream is condensed.

This vessel 11 is connected to the vacuum system 12, which for the sakeof simplicity is shown consisting only of one steam ejector and onecondenser 14. Usually, the desired vacuum value in the plant is achievedby a number of steps each comprising a steam ejector and a condenser. Atthe outlet of the condenser 14 there is a pump 15 which transportsnon-condensable gases to a mass flow meter 16. This mass flow metersenses the amount of gas, which leaves the plant. The amount of gas isregistered and if the amount of gas increases there will be an alarm. Anincreased gas flow during treatment of the oil indicates that there issomething wrong with the equipment or with the processing conditions.

What is claimed is:
 1. A method to monitor the vacuum conditions inequipment during the processes of refining, bleaching and/ordeodorization, during which treatment a number of process steps arecarried through under vacuum achieved by a vacuum system, the methodincluding the steps of sensing the mass flow of non-condensable gas outfrom the vacuum system; and registering the mass flow of non-condensablegas out of the vacuum system for the treatment of vegetable or animaloil.
 2. Method according to claim 1, including the further steps oftriggering an alarm when an amount of gas differing from a set valueduring operation conditions is detected.
 3. Apparatus for carrying outthe method of claim 1, said apparatus comprising equipment which is keptunder vacuum by a vacuum system (12) having at least one vacuum creatingmeans (13) and at least one condenser (14), and a pump (15) arranged atthe outlet of the condenser which is connected to a mass flow meter (16)monitoring the mass flow of a gas and generating signals receivable by acontroller in response thereto.